The invention relates to a method and a device for preventively actuating vehicle occupant protection elements in a vehicle, in particular reversible elements, which include a vehicle movement dynamics control system, in which an evaluation variable relating to a state of “oversteering” is monitored and when the state of “oversteering” is identified the vehicle occupant protection elements are activated.
The prior art, such as German Patent Document DE 101 21 386 C1 discloses a method for actuating a reversible vehicle occupant protection element in a vehicle with a sensor system which senses driving state data, and with a reversible vehicle occupant protection element which can be triggered before the collision time and thus placed in an operative position, wherein the driving state data is monitored with respect to a state of “emergency braking” and when a state of “emergency braking” is determined the vehicle occupant protection element is triggered. According to embodiments of the present invention, the driving state data is additionally monitored with respect to a state of “oversteering” and a state of “understeering” and when a state of “emergency braking” and/or “oversteering” and/or “understeering” is determined the vehicle occupant protection element is triggered. The direction from which a maximum hazard is to be expected is determined by using the states of “emergency braking”, “understeering” and “oversteering”, and the vehicle occupant protection element is actuated in such a way that the protective effect is provided according to the direction of maximum hazard.
In this embodiment, the state of “oversteering” is determined by evaluating the attitude angle which is determined from the wheel speeds, the yaw rate and the transverse acceleration. In an alternative embodiment, the state of “oversteering” is determined by evaluating the difference between an angle which describes a change in the actual direction of travel and the steering angle, with the angle which describes the change being determined from the wheel speeds, the wheel base, the transverse acceleration and/or the yaw rate. This difference corresponds physically to the setpoint yaw moment of the vehicle. The necessary evaluations are carried out in all cases by using a threshold value comparison, which includes a predefinable, fixed threshold value.
In this method, the determination of the variable which is to be evaluated for oversteering, that is to say the attitude angle or alternatively the difference in the angle which describes the change in the actual direction of travel and the steering angle, is relatively complex and in the case of the attitude angle the variable is additionally subject to a relatively imprecise estimation.
One object of the invention, therefore, is to provide an improved method and a device of the type described above by which it is possible to detect oversteering with little expenditure.
This and other objects and advantages are achieved by the method and apparatus are to the invention, for actuating occupant protection elements using a vehicle movement dynamics control system. In order to preventively actuate vehicle occupant protection elements, in particular reversible elements which can be activated before a collision time and thus placed in an operative position, an evaluation variable relating to a state of “oversteering” is monitored. When a state of “oversteering” is identified the vehicle occupant protection element is activated, wherein a manipulated variable is determined by a vehicle movement dynamics control system of the vehicle; and the evaluation variable for monitoring the state of “oversteering” is determined by using the manipulated variable.
The advantage of this method is that the manipulated variable of the vehicle movement dynamics control system has a particularly precise and sufficiently reliably determined variable in which essentially all the possible driving situations, for example for travel around steep bends and special driving maneuvers of the vehicle are taken into account. No measures are necessary for sensor calibration or the like since all the necessary sensor calibration and monitoring processes are carried out by the vehicle movement dynamics control system.
In one preferred embodiment, the manipulated variable corresponds physically to a setpoint yaw moment which is determined by the vehicle movement dynamics control system. This ensures that the evaluation variable also corresponds to the setpoint yaw moment. Therefore, a variable which has already been determined, such as the setpoint yaw moment of the vehicle movement dynamics control system, and which is determined particularly easily and quickly, is available for monitoring the state of “oversteering”. In this example, a high value of the manipulated variable is an indicator of severe oversteering or of imminent severe oversteering of the vehicle.
The setpoint yaw moment is preferably a manipulated variable from which brake pressures which are to be applied selectively at individual wheels can be determined. This permits the vehicle occupant protection elements to be activated as a reaction to situations in which the brake pressures of individual wheels are corrected. Such corrections by the vehicle movement dynamics control system take place in particular in states of oversteering.
One advantageous embodiment provides that a value of an evaluation function of a fuzzy logic is determined for the manipulated variable as an intermediate variable. This permits stepless evaluation and actuation of the vehicle occupant protection elements. The evaluation function preferably has a value range from 0 to 1 or any other desired value range which corresponds to the physical variable and the measurement range of the manipulated variable.
In a further embodiment, a result of low-pass filtering of the intermediate variable is determined as an evaluation variable. The low-pass filtering is preferably carried out asymmetrically. In this exemplary embodiment, the low-pass filtering has a rapid rise and a slow decline. As a result, in the case of brief interventions, an activation signal which is present for a sufficiently long time is also made possible.
A preferred embodiment provides for the state of “oversteering” to be identified if the monitoring reveals that the evaluation variable exceeds a first threshold value, for example “1”. Monitoring to determine whether the first threshold value of the evaluation variable is exceeded is a simple possible way of identifying the state of oversteering.
A further preferred embodiment provides for the state of “oversteering” to be rejected and for the triggered vehicle occupant protection elements to be deactivated if the monitoring reveals that the evaluation variable undershoots a second threshold value, for example “0”.
For example, the first threshold value is higher than the second threshold value. As a result, a hysteresis is run through in relation to the activation and deactivation of the vehicle occupant protection elements.
It is advantageous if at least one of the threshold values is adapted as a function of at least one further parameter. This permits in particular the activating first threshold value to be adapted to the driving situation, for example to the speed of the vehicle. It is thus possible to model the sensation of risk of a user of the vehicle. The user generally feels safe at low speeds of the vehicle and low coefficients of friction so that the activating first threshold value can assume a relatively high value. At high speeds of the vehicle and high coefficients of friction, the subjective sensation of risk is generally more pronounced so that the triggering threshold value then advantageously assumes a lower value.
A lateral acceleration and/or a resulting overall acceleration and/or a coefficient of friction which is actually used and/or the speed of the vehicle are expediently used as a further parameter. At a high coefficient of friction, such an embodiment of the system of actuating a preventive-action vehicle occupant protection element can thus lower the first threshold value, which is assigned to a driving situation such as the state of “oversteering” which is critical in terms of transverse dynamics. This leads, in particular, at high speeds of the vehicle compared to a conventional preventive-action vehicle occupant protection system, to an increase in the number of activations of the vehicle occupant protection elements, as a result of which the acceptance of the preventive-action vehicle occupant protection system with a user of the motor vehicle is under certain circumstances increased.
The device according to the invention has a vehicle movement dynamics control system, a control unit, and vehicle occupant protection elements, which can be reversible. The exemplary control unit can determine an evaluation variable by using a manipulated variable which is determined by the vehicle movement dynamics control system, and to identify, by using the evaluation variable, whether a state of “oversteering” is present, and it being possible to trigger the vehicle occupant protection elements automatically if the control unit identifies the state of “oversteering”. The manipulated variable of the vehicle movement dynamics control system preferably corresponds physically to a setpoint yaw moment.
In one particular embodiment, the control unit outputs a signal which corresponds to the identified state. In this way, the information about the state of “oversteering” is also available to other vehicle devices, for example for performing open-loop and/or closed-loop control of other operating functions of the vehicle.
The device preferably has a data bus, in which case the control unit transmits the signal onto the data bus. The information about the state of “oversteering” can thus be called via a standard interface.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.